The present invention relates to parallel hybrid electric vehicles comprising an engine and a motor which also serves as a generator, wherein output torques of the two are transferred to a transmission through a torque combining mechanism comprising a differential gear so as to obtain traction by means of one or both of the engine and the motor.
In a typical parallel hybrid electric vehicle, output torques of the engine and the motor/generator are combined through a torque combining mechanism comprising a planetary-gear set, which is transferred to driving wheels through a transmission. The vehicle carries out starting acceleration, for example, with combined output torques of the motor/generator and the engine. In a higher-speed range, the vehicle cruises using only engine output torque with the motor/generator turned off. Specifically, when the number of revolutions of the motor/generator reaches that of the engine, the two, and more specifically, elements of the planetary-gear set coupled with the two, are directly coupled with each other through an engagement device such as clutch, allowing vehicle cruising only with engine torque. At vehicle deceleration, the motor/generator is rotated with road reaction torque to serve as a generator for power accumulation, achieving regenerative operation so called. That is, the parallel hybrid electric vehicle aims to achieve more efficient cruising, e.g. higher accelerating force and lower fuel consumption, by controlling the operating conditions of the motor/generator, i.e. number of revolutions and output torque.
In the above parallel hybrid electric vehicle, at starting from a standstill, for example, the engine speed is restrained at a predetermined value to generate normal-direction torque or vehicle accelerating direction in the motor/generator for vehicle starting. When the number of revolutions of the motor/generator coincides exactly or roughly with that of the engine, input shafts of the engine, motor/generator, and automatic transmission are directly coupled with each other through engagement of the engagement device. At engagement of the engagement device, torsional vibrations occur in the drive system, which are transferred as discomfort vibrations to a passenger or occupant. This problem occurs even when a one-way clutch for allowing one-direction rotation serves as the engagement device.
It is, therefore, an object of the present invention to provide parallel hybrid electric vehicles which contribute to restraint of vibrations at engagement of the engagement device.
The present invention provides generally a parallel hybrid electric vehicle which comprises: an engine; a motor/generator having functions of a motor and a generator; a transmission; a differential gear comprising a first shaft connected to an output shaft of the engine, a second shaft connected to an output shaft of the motor/generator, and a third shaft connected to an input shaft of the transmission; an engagement device interposed between two of the first to third shafts of the differential gear, the engagement device being engaged when a difference in number of revolutions between the engine and the motor/generator is smaller than a predetermined value at starting of the vehicle; and an electronic control unit (ECU) which controls operating conditions of at least one of the engine and the motor/generator, wherein when the difference in number of revolutions is smaller than the predetermined value, the ECU sets a predetermined torque correction amount in accordance with a relationship between an inertia of the engine and that of the motor/generator, and wherein the ECU carries out a correction of torque of one of the engine and the motor/generator in accordance with the predetermined torque correction amount as set.
A main feature of the present invention is to provide a parallel hybrid electric vehicle which comprises: an engine; a motor/generator having functions of a motor and a generator; a transmission; a differential gear comprising a first shaft connected to an output shaft of the engine, a second shaft connected to an output shaft of the motor/generator, and a third shaft connected to an input shaft of the transmission; an engagement device which carries out engagement and release between two of the first to third shafts of the differential gear; and an ECU which, at starting of the vehicle, puts the engagement device in a non-engaged state and controls torque of the motor/generator to maintain a number of revolutions of the engine at a predetermined number, wherein the ECU puts the engagement device in an engaged state when numbers of revolutions of the first to third shafts of the differential gear agree at least substantially with each other, and wherein the ECU carries out one of the following operations of: decreasing the torque of the motor/generator at engagement of the engagement device when an inertia of the motor/generator is smaller than a value obtained by multiplying an inertia of the engine by a gear ratio of the differential gear; increasing the torque of the motor/generator at engagement of the engagement device when the motor/generator inertia is larger than the value; increasing the torque of the motor/generator at engagement of the engagement device when the motor/generator inertia is smaller than the value; and decreasing the torque of the motor/generator at engagement of the engagement device when the motor/generator inertia is larger than the value.